1. Field of the Invention
The present invention relates to a unit type starting clutch which can be fitted with respect to a torque converter of an automobile and the like.
2. Description of the Related Art
Conventionally, in automatic transmissions i.e. ATs, the starting of a vehicle was performed by torque transmitting through a torque converter. The torque converter was mounted to many AT vehicles since the torque converter has a torque amplifying effect and provides smooth torque transmission.
On the other hand, the torque converter has a disadvantage that a large amount of slip is generated during the torque transmission and, thus, the torque converter has less efficiency.
Therefore, in recent years, there has been proposed a technique in which a starting clutch is used in place of the torque converter, and the torque has been amplified at a low speed range by reducing a gear ratio and by increasing the number of speed change stages.
In general, the starting clutch includes a wet type multi-plate clutch housed in a clutch case. In the multi-plate clutch, friction plates as friction engaging elements at an output side and separator plates as friction engaging elements at an input side are arranged alternately along an axial direction. With this arrangement, a power is transmitted by engaging the friction plates with the separator plates by means of a piston.
In the starting clutch, particularly when the vehicle is operating under heavy traffic conditions, engagement and disengagement of the clutch are repeated frequently, causing heat to accumulate in the clutch portion, and thus requiring a large amount of lubricant oil to be supplied to the clutch portion. However, power loss caused by a pump for supplying the large amount of lubricant oil adversely impacts the reduction of fuel consumption.
In the wet type starting clutch, when the vehicle begins to start, i.e., when the wet type multi-plate clutch is engaged, a maximum amount of heat is generated. Conventionally, in order to cool such heat, a large amount 10 liters/min or more) of lubricant oil was always supplied. In the wet type multi-plate clutch, the lubricant oil is required to perform the cooling upon the engagement of the clutch, and the lubricant oil is also required to cool the heated clutch having a high temperature during an idle rotation of the clutch. In general, during the engagement of the clutch, since it is difficult for the supplied lubricant oil to flow between the plates of the clutch, even if the lubricant oil is supplied, it is difficult to cool the clutch.
To address such a problem, for example, Japanese Patent Application Laid-open No. 2004-324818 discloses a technique in which the lubricant oil is supplied in accordance with a condition of the vehicle by using an electronic hydraulic solenoid. However, in this technique, the large amount of the lubricant oil is supplied to the clutch during a slipping condition of the clutch, and, if the engagement and disengagement of the clutch is repeated frequently, adequate cooling cannot be achieved.